Learn Chemistry
First Year Undergraduate Chemistry
Laboratory Course Manual 2011-2012
Core Chemistry 1A and 1B: Skills Block 1
Developed by Dr Jacquie Robson, RSC School Teacher Fellow 2010-2011 at Durham University
This resource was produced as part of the National HE STEM Programme
www.rsc.org/learn-chemistry
Registered Charity Number 207890
Core Chemistry 1A and 1B
First Year Chemistry
Laboratory Course
Manual 2011-2012
SKILLS
BLOCK 1
Name ……………………………………………………………………………….
Core Chemistry 1A session:
Day/Time: ………………………………… Group name: ….……….....
Core Chemistry 1B session:
Day/Time: ………………………………… Group name: …….…………
Contents
Page
Safety in the first year laboratory (CG 021) ........................................................................................... 3
Introduction ........................................................................................................................................... 5
2A. Investigating concepts of evidence: how much water can a paper towel soak up? .................... 11
2B. Understanding and using evidence: does volume of water affect time taken to dissolve sugar? 19
3A. Determination of the Mr of an unknown solid acid using titration .............................................. 23
3B. Determination of the % purity of a sample of oxalic acid (ethanedioic acid) ............................... 29
4A. Purification of an unknown solid by recrystallisation ................................................................... 33
4B. Preparation of cyclohexene ........................................................................................................... 39
APPENDIX A: Assessment guide for laboratory reports ...................................................................... 44
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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Safety in the first year laboratory (CG 021)
The Health and Safety at Work Act was introduced in 1974. Since then many regulations have been
made under the act, for example, The Control of Substances Hazardous to Health (COSHH). The
University has a statutory obligation to comply with these requirements and you, as a student, have
a duty to abide by the regulations. The following notes are to guide you in good laboratory practice
and to familiarise yourself with the safety aspects of your laboratory work.
Emergency Telephone Numbers
Internal telephones: FIRE, POLICE, AMBULANCE
9999
UNIVERSITY EMERGENCY NUMBER 43333
1.
Staff with special responsibilities for safety:
Chairman of the Board of Studies:
Professor J S O Evans
Chemistry Safety Officer:
Dr J A G Williams
Undergraduate teaching laboratories:
Dr E Wrede (Physical Chemistry)
Dr J A G Williams (Inorganic Chemistry)
Dr E Khosravi (Organic Chemistry)
2.
No work is to be carried out unless a member of staff is present.
3.
All persons in laboratories (whether or not they are actually doing practical work) must wear
safety spectacles and laboratory coats. Academic staff supervising undergraduates enforce
this rule. In all laboratories, hair should be secured so that it does not hang below the neck.
It is important to wear suitable clothing, and your footwear must incorporate flat heels, slipresistant soles and uppers fully enclosing the foot.
4.
Foods, drinks, cosmetics and cigarettes must not be taken into or used in areas where
chemical substances are used or kept.
5.
Bags and coats should be placed in the lockers provided outside the laboratory and not left
in corridors or on benches.
6.
All accidents and dangerous occurrences must be reported immediately to a member of
staff or a demonstrator. The first aid box is located in the foyer area and a list of qualified
first aiders is on the front. The accident book is kept in room CG 058 and the member of
staff in charge of the laboratory must fill out a report for all incidents. An emergency shower
is located in the foyer area and there are four eyewash stations beside the sinks. There is a
chemical spillage treatment kit in CG195.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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7.
The fire action signs in the laboratory indicate the nearest fire alarm and the emergency
exit. There are two carbon dioxide fire extinguishers on either side of the central pedestal
and another in the instrument room. There is also a foam spray fire extinguisher on either
side of the central pedestal and one at each fire exit. A general fire practice is held twice
yearly to check the smooth operation of the procedure so you should ensure that you know
where to go in an emergency.
8.
Pipetting by mouth is not allowed. Use a bulb or automatic pipette.
9.
Do not inhale vapours or make skin contact with any substances. Use gloves where
necessary always remembering that they are semi-permeable.
10.
Experiments must be conducted on clean working surfaces; any spillage should be cleaned
immediately. A high standard of tidiness should be maintained at all times. Contaminated
surfaces and equipment must be cleaned as soon as it is practicable after use. The
equipment should then be put away. Do not clutter bench-space with unused equipment
and bottles of chemicals.
11.
Waste should be disposed of in the appropriate containers: solvents should be placed in
either C, H, N, O-containing waste solvent bottles (Category C Waste), or halogen, sulphurcontaining waste solvent bottles (Category D Waste). Heavy metal waste should be placed in
the appropriate bottle. Broken glassware should be washed and placed in the designated
glass bin. Solid waste should be dried, placed in a polythene bag and placed in a solid waste
bin. A sharps bin is located in CG195. Consult a demonstrator if you are unsure about the
correct disposal procedure.
12.
The COSHH assessment of any chemical you use or make will be given in the laboratory
script. There are further safety warnings at the appropriate parts of the text. Staff and
student demonstrators reinforce these. If you are in any doubt, consult a demonstrator.
13.
No unauthorised experiments are to be carried out.
14.
It is important to ensure that hands are washed and all protective clothing removed before
leaving the laboratory.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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Introduction
Chemistry is an experimental science and, as well as attending lectures, both the University and the
Royal Society of Chemistry, who accredit your degree, require you to complete a designated
number of hours of laboratory work. During the first year, 18 weeks of practical work must be
completed. The first year practical course is split into four sections:
1. Induction (Week 1)
2. Skills (Weeks 2-7)
3. Discovery (Weeks 8-16)
4. Projects (Weeks 18-19).
During the next six weeks, you will complete the Skills section. This contains activities designed to
ensure that you are familiar with, and have practised, some of the key skills required in the
chemistry laboratory. Some of these will be familiar to you from your pre-University studies, but
this will vary from person to person. This section will also introduce the various resources you can
use in your own time, away from the laboratory, to ensure you are confident in your work and
make the most of your time in the laboratory.
1.1 The pre-lab exercises
Before every laboratory session, one or more pre-lab exercises must be completed. These may
involve reading, watching video clips, answering questions or using interactive software to rehearse
techniques. The instructions for these exercises will be accessed via DUO, the university Virtual
Learning Environment. Becoming familiar and comfortable with the use of DUO is one of the aims
of this section.
Pre-lab exercises will often contain summative aspects (i.e. the marks will count towards the overall
marks for the Laboratory Course), and they must be completed in the week before you attempt the
laboratory activity. All pre-lab work must be finished an hour before the relevant laboratory session
so that completion can be checked. For example, a student attending the Thursday laboratory
session, which begins at 2.00pm, must have completed the pre-lab exercises by 1.00pm that same
day. Anyone arriving at a laboratory session without having completed the pre-lab exercises will be
sent away to complete them before being allowed to begin work in the laboratory. Failure to
complete the pre-lab exercises on time will incur a marks penalty. Your time in the laboratory will
become very pressured if you are sent away to complete the pre-lab exercises. Good time
management is the key to success in most areas of university life, but particularly in your laboratory
work!
If there are any problems with access to DUO or LabSkills using personal computers, there are
open-access machines available for use in the library and at other points around the science site.
There may also be provision in college. Ask for help if problems arise when accessing the pre-lab
exercises. Failure to access the exercises will not be accepted as a reason for incomplete pre-lab
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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work unless the laboratory course leader (Dr J. M. Robson) is informed in advance of the deadline
so alternative arrangements can be made.
1.2 LabSkills
Many pre-lab exercises will involve you using LabSkills. This is an electronic laboratory textbook for
you to use to gain confidence in assembling and using apparatus before you begin work in the
laboratory. Interactive exercises are designed to allow you to practice key techniques and learn
more about apparatus and safety as you progress through the course. During the Skills section of
your laboratory course, the pre-lab exercises will be very prescriptive in their use of LabSkills. You
can, however, access it at any time during your undergraduate career at Durham to refresh your
memory of any basic techniques and skills before any practical class. LabSkills also contains useful
glossaries and worked examples of calculations that you will find useful. It will be accessible in the
laboratory for additional assistance if you need it.
1.3 The laboratory sessions
One laboratory session per week will be assigned to Core Chemistry 1A, and a second session per
week for Core Chemistry 1B. Experiments that will count towards Core Chemistry 1A will contain a
suffix of ‘A’ in the title (e.g. Experiment 3A) and will be carried out by everybody. Experiment titles
containing a suffix of ‘B’ (e.g. Experiment 3B) will count towards Core Chemistry 1B and will be
carried out only by those studying Core Chemistry 1B.
In this term (Michaelmas), University weeks begin on a Thursday and end on a Wednesday. Those
students only studying Core Chemistry 1A will be assigned one laboratory session per week and will
carry out all of the ‘A’ experiments. Those students also studying Core Chemistry 1B will be
assigned two sessions per week. The first session of the week is assigned to be the Core Chemistry
1A session, and the second session of the week is the Core Chemistry 1B session. For example, if
the two allocated laboratory sessions are on Thursday morning and Monday afternoon, the Core
Chemistry 1A session will be Thursday morning, when an experiment with the suffix ‘A’ will be
performed, and the Core Chemistry 1B session will be Monday afternoon, when the ‘B experiment
for that week will be completed.
Laboratory sessions will be allocated during one or two of the following times:
Thursday
9.00am - 12.00pm
Friday
9.00am - 12.00pm
Friday
2.00pm - 5.00pm
Monday
9.00am - 12.00pm
Monday
2.00pm - 5.00pm
Tuesday
2.00pm - 5.00pm
Wednesday 10.00am - 1.00pm
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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You may only attend the laboratory at your allocated time. A risk assessment is provided in this
manual for the chemicals used in each experiment. This must be read carefully before attending the
laboratory, and the advice followed throughout each laboratory session. All experimental work
must be completed in that laboratory session and your lab notebook and work space signed off
before you leave.
1.4 Set allocation
Students in each laboratory session are allocated to one of three named sets of no more than 20
students. Sets are named after chemical elements and students are assigned to sets in no particular
order. Lists showing members of each set are available on DUO and details should be written onto
the front of the laboratory manual. Each set will tackle a different activity each week, in a three
week cycle, until everyone has completed each activity. The three experiments in the laboratory
will then change and each set will again work through each experiment according to the rota.
Set names are as follows:
Thurs am
Friday am
Friday pm
Monday am
Monday pm
Tuesday am
Wed am
Set 1
actinium
dysprosium
gadolinium
potassium
niobium
rhodium
uranium
Set 2
Set 3
bismuth
cobalt
erbium
fluorine
hafnium
yttrium
lithium
molybdenum
phosphorus
osmium
strontium
tantalum
vanadium
tungsten
Students will be allocated one set for their Core Chemistry 1A session and a second set for their
Core Chemistry 1B session. Set lists will appear on DUO before the start of Week 2. Sets will
perform experiments according to the following rota:
Week
2
3
4
Set 1
Experiment 2
Experiment 3
Experiment 4
Set 2
Experiment 3
Experiment 4
Experiment 2
Set 3
Experiment 4
Experiment 2
Experiment 3
For example, in week 3, everyone in Set 2 will carry out Experiment 4. Those studying only Core
Chemistry 1A will only complete Experiment 4A. Those students also studying Core Chemistry 1B
will complete Experiment 4B during their second session of the week. During Week 1, you will find
out your allocated sets and should write the details onto the front of your laboratory manual.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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1.5 Assessment
Pre-lab exercises, mostly carried out via DUO, will contain assessed components. These exercises
will differ between experiments, but assessed aspects will be highlighted. Completion of these
exercises is compulsory and there will be a marks penalty for non-completion. The pre-laboratory
exercise marks will make up 10% of the total marks for the practical course.
During each laboratory session, work and progress will be assessed. Completion of the lab
notebook and performance in the practical tasks will be given marks. Occasionally there will be a
small amount of post-laboratory work that will need to be completed to finish each experiment.
Marks will be awarded during laboratory sessions throughout the year and will make up 10% of the
total marks for the practical course.
In the Skills section, the focus is on the development of a good general technical skill base to be
used throughout your practical work at University. There will be one small additional assessed
written exercise for those students studying Core Chemistry 1B. From Week 8 onwards, in the
Discovery and Projects sections, there will be additional assessed exercises for all students that will
count towards your total marks for the practical course.
1.6 Assessment summary
Pre-lab exercises (whole year)
Laboratory session marks (whole year)
SKILLS Experiment 5B:
Determination of the enthalpy of vaporisation of ethanol
DISCOVERY Experiment 10A
DISCOVERY Experiment 10B
DISCOVERY Experiment 11B
DISCOVERY Experiment 12A
DISCOVERY Experiment 15A
DISCOVERY Experiment 15B
PROJECT
Core Chemistry
1A
10 %
10 %
-
Core Chemistry
1B
10 %
10 %
5%
20 %
15 %
20 %
20 %
20 %
20 %
20 %
20 % *
100 %
100 %
*For students completing both Core Chemistry 1A and Core Chemistry 1B, 50 % of the project mark
will be allocated towards the Core Chemistry 1A total marks, and 50 % will be allocated towards the
Core Chemistry 1B total marks.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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1.7 Supervising staff and postgraduate demonstrators
SKILLS Block 1 – week 2 to week 4 (Thursday 13th October to Wednesday 2nd November 2011)
Senior Demonstrators (staff)
Dr Jacquie Robson*
Dr Pippa Coffer
Dr Ehmke Pohl
Junior Demonstrators (postgraduate students)
Jonathan Coome
Alex Dudgeon
Rebecca Edwards
Ricardo Girling
Helen Mason
Hannah Straker
Julie Thye
* Laboratory course leader - email: [email protected]
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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SKILLS
BLOCK 1
EXPERIMENT 2A
INVESTIGATING CONCEPTS
OF EVIDENCE:
HOW MUCH WATER CAN A
PAPER TOWEL SOAK UP?
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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SKILLS
EXPERIMENT 2A
2A. Investigating concepts of evidence: measuring how much water a paper towel
can soak up?
An understanding of how experiments are designed and structured and ideas about reliability,
causality and validity are essential to enable critical evaluation of scientific information. These ideas
are touched upon in school science curricula but a thorough understanding of these essential
concepts can take time and practice to fully appreciate.
Designing an experiment requires much scientific understanding. All the ideas detailed above need
to be carefully considered and the design adapted and refined after testing to produce a procedure
that gives good quality evidence or data. Many of the scientific techniques that often need to be
learned by rote, such as titration, are protocols developed by previous scientists, with consideration
for these key ideas, to ensure that the data produced are of the highest possible quality. Designing
a new experimental method is a very different skill to carrying out a learned protocol. This activity
allows that skill to be practised with a focus on the processes involved. Experiments are designed to
allow the collection of evidence or data. Measurement is central to the collection of scientific
evidence, but how a measurement is carried out and the choice of the apparatus used is key to
understanding the quality of the evidence.
This activity, set in a very simple context, allows the exploration of some of these issues. Treatment
of data, using the mean, the range, the standard deviation and the standard error, is also
investigated.
Think carefully about each step of this activity. Try not to focus on the outcome, but on the
reasoning behind any experimental decisions or assumptions made. Different people within a
group, and different groups, will come up with different ideas to tackle this exercise. This is
encouraged as the discussion around each idea is essential to develop understanding. There is no
single right answer or expected outcome for this activity, although some methods may give better
quality data than others. Learning about and understanding the planning process and the ideas
detailed above is the desired outcome. The aim is to develop understanding of some key ideas
about data, evidence, measurement and experimental design by exploring many different
possibilities.
2A.1 Aims
 To design and carry out a simple procedure to answer a question
 To develop understanding of the ideas behind experiment design and measurement
 To discuss and develop understanding of the use of mean values, ranges, standard
deviations and standard errors in reporting experimental findings
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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2A.2 Pre-lab exercises
These exercises must be completed at least one hour before the timetabled start time of the
laboratory session. Students not completing the pre-laboratory task will be turned away from the
laboratory until the exercises are completed.
If carrying out this activity in Week 2, ensure that all the post-lab exercises from the first laboratory
session are completed. This includes setting up the lab notebook ready for use.
Reading exercise:
1. Read through all experimental instructions given in the laboratory manual.
2. Read Gott, R. and Duggan, S. “Understanding Scientific Evidence – How to critically evaluate
data” 2003, Sage Publications, London, Thousand Oaks, New Delhi. The full text is available
to all Durham students via the University Library web pages (follow the link on DUO). Ensure
that Chapters 2, 3, 6, 7 and 8 are read particularly thoroughly and used to explain any
unfamiliar terms in the experiment instructions.
Make sure you understand the following terminology (page numbers refer to Gott and Duggan.
Additional information is available in the National Physics Laboratory ‘Beginner’s Guide to
Uncertainty of Measurement’ by Stephanie Bell (1999), available via DUO).
 validity and reliability (p6-7)
 precision (p117-119)
 accuracy (p119-123)
 standard deviation (p143-149)
 standard error (p149-p152)
Use the ideas presented in the book to inform any decisions made during the next task. To get the
most out of the laboratory activity and the discussions, it is essential that the reading has been
done properly before arriving in the laboratory.
Planning exercise:
Available apparatus:
 thermometers
 stopwatches
 measuring cylinders of various sizes
 beakers of various sizes
 droppers
 pipettes
 top pan balances
 funnels
 paper towels
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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Using apparatus from the list and any other available laboratory apparatus, design a simple
procedure to determine how much water a paper towel can soak up. Describe equipment sizes and
volumes. Think about the reasons behind the selection of particular apparatus or any particular
scale (i.e. what volumes of liquids to use) and consider the ideas presented in the textbook when
making these decisions. Prepare the next page of the lab notebook for use in the session, and write
the method in. Design and draw a results table in the lab notebook to contain the data to be
collected.
A demonstrator will check that you have completed this task before you will be allowed to join the
rest of your group to begin the laboratory activity.
2A.3 Laboratory activity
Suggested timings are given for each part of the activity to ensure that groups complete the activity
on time.
(30 minutes)
In groups of three or four, each group member is to take turns to present the procedure that was
designed in the pre-lab. Discuss the strengths of each procedure, identify any possible areas for
improvement and consider any issues or difficulties that each particular method may present.
Discuss the validity of the method and any attempts to ensure precision, accuracy and reliability.
Remember, there is no single right answer here and it is to be expected that there will be up to four
different procedures to discuss, not four versions of an identical method! This exercise is not about
identifying which method is ‘correct’, but about considering a number of different ways of
approaching the same problem and considering different aspects of these approaches.
After all procedures have been presented, decide, as a group, which one is the:
 most imaginative
 most complex
 simplest
 fastest method to produce 10 pieces of data
(20 minutes)
Once all of the methods have been considered and ideas about experimental design have been
discussed, a single method should be decided upon. This could be one that has already been
presented, or could be a new method designed after discussion of the strengths of the different
procedures. This agreed method should be reported in the lab notebook of each group member.
Note down any decisions that have been made, with reasons, about the experimental design,
including any assumptions that have been made or any definitions that have been decided upon.
Show a demonstrator your method before moving on to the next part.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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(45 minutes)
Working efficiently in groups, collect at least 10 pieces of data using the agreed method. Adapt the
design if required to ensure the data are as good quality as they can be for the method used, but do
not use unnecessarily precise equipment. Ensure that there are a minimum of 10 pieces of data for
the experiment, recorded in lab notebooks in an appropriate table. Remember that each member
of the group needs a record of the data. Show a demonstrator the results before moving on to the
next part.
(45 minutes)
Each group should now have 10 pieces of data (x1, x2, x3 … x10) which should show variation (i.e.
they will not all be the same). Having a number of different pieces of data representing the
measure of a single thing is usual and common in science. To be able to report a single value (i.e.
one single number that represents all 10 pieces of data), some statistical treatment of the numbers
is required. The first calculation usually performed on a data set is the determination of a mean
value. The best estimate for a single value of x is given by the arithmetic mean. The formula for
calculating the arithmetic mean from n data points is:
n
xi

x1  x2  ... xn
i 1
x
or x 
n
n
Individually, calculate the arithmetic mean for the data set and determine the range of the data.
Compare the values with that calculated by the rest of the group and discuss the following, noting
findings in the lab notebook:
1. Did everyone choose to use all 10 pieces of data or were some ignored? Why?
2. What information does a mean value give about the data?
3. If the mean value alone is reported, is it a true reflection of the findings from the
experiment?
4. Were the data ‘good enough’ to draw a conclusion for this experiment? Decide upon criteria
for ‘good enough’.
Show a demonstrator your findings before moving on to the next part.
Each individual value deviates from the mean by di where: di = xi - x
Note that di can be both positive and negative and that:
n
d
i 1
i
0
It is usual to report the standard deviation (usually given the symbol s or σx) from the mean. This is
the square of the individual deviations for each piece of data, divided by n-1, where n is the number
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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of measurements. The value n-1 is used, rather than n, for good statistical reasons.1 Use the
formula below to calculate the standard deviation for the data set:
x 
1 n
1 n
2
2
.  di  
.  xi  x 
n  1 i 1
n  1 i 1
where σx = standard deviation of the sample
xi = a single measurement
x = mean
n = number of measurements / sample size
Compare the values within the group to check the calculation. Discuss the following within the
group, noting findings in the lab notebook:
1. What information does the standard deviation give about the data that has been collected?
2. What would the data set ‘look’ like if the standard deviation was larger?
3. What would the data set ‘look’ like if the standard deviation was smaller?
4. In what way is reporting a mean with a standard deviation more useful than reporting a
mean and a range?
5. What are the limitations of reporting a standard deviation?
Tell a demonstrator your findings before moving on to the next part.
The mean value represents the average of a distribution of 10 different values. The standard error
(often referred to as the ‘standard deviation of the mean’) is also often reported as it gives a
measure of the precision to which x is known. Calculate the standard error for the data. The
mathematical formula for the standard error is:
SE 
x
n
where SE= standard error (sometimes shown as  x )
σx = standard deviation
n = the number of readings
1
For a more in-depth explanation, see p87 of Taylor, J. R., ‘An Introduction to Error Analysis: The Study of Uncertainties
in Physical Measurements’, (1982), University Science Books.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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Discuss the following within the group:
1. What different information does the standard deviation and the standard error give about a
particular data set?
2. What does the value of the standard error tell us about the data?
3. What simple change could be made to the experiment design to reduce the standard error?
4. Make a claim about the data collected by the group (e.g. How much water can a paper
towel soak up?). Consider the mean, the standard deviation and the standard error when
reporting your findings.
5. Are the claims of other groups likely to be the same? Why? What are the limitations of the
groups’ claim?
Report the group’s findings to the demonstrator for discussion.
Use of Excel to calculate mean, median, mode, standard deviation and standard error:
Open Excel on one of the laboratory computers and input the group’s data set (all 10 pieces of
data) in one column. Click on the ‘Data Analysis’ tab and select ‘Descriptive Statistics’. Use the
mouse to highlight the data. This should show in the ‘Input Range’ box. Click for a new worksheet
to be generated and tick ‘Summary Statistics’ box. Clicking OK will generate a table on another
sheet that shows the mean, standard error, median, mode and standard deviation (among other
things) for the data. Compare the values to those you calculated. This tool can be used in Excel to
analyse data sets collected during other practical work in this course.
Tidy up the work area and put equipment away. Show a demonstrator the lab notebook to be
signed off before leaving the laboratory.
2A.4 Post-laboratory work
Review the Gott and Duggan textbook after the session to consolidate your learning during the
laboratory activity. This book is available for open access by members of the University via the
library website (the link is available on DUO):
Gott, R. and Duggan, S. “Understanding Scientific Evidence – How to critically evaluate data” 2003,
Sage Publications, London, Thousand Oaks, New Delhi.
You should also review the National Physics Laboratory Measurement Good Practice Guide No. 11:
Beginners Guide to Uncertainty in Measurement by Stephanie Bell (1999), available on DUO.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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SKILLS
BLOCK 1
EXPERIMENT 2B
FURTHER INVESTIGATION OF
CONCEPTS OF EVIDENCE:
DOES THE VOLUME OF WATER
AFFECT THE TIME TAKEN TO
DISSOLVE SUGAR?
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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SKILLS
EXPERIMENT 2B
2B. Understanding and using evidence: does the volume of water affect the time
taken to dissolve sugar?
In the previous laboratory session, important aspects of experimental design and data analysis
were considered. This activity will allow for further exploration of these important ideas, and the
opportunity to tackle a more complex problem.
2B.1 Aims
 To design and carry out a simple method to produce evidence to answer a question
 To develop deeper understanding of the ideas behind experiment design and measurement
 To practice good data analysis and graph drawing techniques
2B.2 Pre-lab exercises
These exercises must be completed in the week before the experiment, and completed at least one
hour before the timetabled start time of your laboratory session. You will not be allowed to enter
the laboratory until the exercises are completed.
Reading:
1. Read through all experimental instructions given in the laboratory manual.
2. Review Gott, R. and Duggan, S. “Understanding Scientific Evidence – How to critically
evaluate data” 2003, Sage Publications, London, Thousand Oaks, New Delhi. Link available
on DUO.
3. Re-read the NPL Good Practice Guide No. 11: ‘Beginners Guide to Uncertainty in
Measurement’ by Stephanie Bell (1999), available on DUO.
Take some time to review any sections that are still unclear and consider the whole book again in
light of findings from the first attempt at planning an experiment in the previous session.
Planning:
Available apparatus:
 sieves
 beakers, measuring cylinders and pipettes of various sizes
 thermometers
 stirring rods
 tap water
 teaspoons
 spatulas
 sugar
 top pan balances
 stopwatch/timer
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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Before arriving at the laboratory, think about possible approaches to collecting evidence to try to
answer the question “Does the volume of water affect the time taken to dissolve sugar?” An initial
method to allow attempts at data collection needs to be agreed upon in the first 30 minutes of the
laboratory session. It is expected that this initial method will be developed iteratively as issues arise
during the laboratory session. Lab notebooks should not have a method written in them on arrival
in the laboratory, but they should be prepared (with a date and title) before the session as usual.
2B.3 Laboratory activity
This activity will be carried out in pairs. Choose a work area with a free locker, and write the locker
number at the top of the lab notebook page for this experiment. Inform the demonstrator of the
locker number. In pairs, develop a method to answer the question “Does the volume of water
affect the time taken to dissolve sugar?” The answer to the question (the conclusion) should
include a graph that illustrates the relationship, so discuss what should be plotted on the graph,
and how it should be plotted. To assist with the task, work through the following:
 Decide which is to be the independent and dependent variable.
 How might the variables be measured? (Pay particular attention to selecting apparatus with
appropriate, but not unnecessary, precision).
 List possible other factors that might affect the value of the dependent variable.
 Consider how these other variables will be kept the same throughout the experiment
 Predict what the likely outcome will be. What is the graph of the data likely to look like?
 Use the available apparatus to trial the method as it is developed to check for problems.
Once a method has been developed that is likely to provide enough evidence to answer the
question, write the method into the lab notebook. The answer to the question (the conclusion)
should include a graph that illustrates the relationship, thus discussion should be had within the
pair to decide what should be plotted on the graph, and how it should be plotted. Complete this
exercise in the first 30 minutes of the laboratory session. Show the method to the demonstrator.
Carry out the experiment. Make any adjustments required to the method as the experiment is
performed and note the changes made, with reasons, in the lab notebook. Keep working until both
members of the group are satisfied that enough data have been collected to produce a graph and
draw a conclusion.
Using graph paper, plot a graph of the data (individually) and write a conclusion about the
experiment. Show completed graphs to the demonstrator. The demonstrator will discuss the
outcome of the experiment with each pair, and will help decide whether or not an alternative
method or more data collection is required, or whether the results are sufficient.
Once the demonstrator is satisfied with the outcome of the experiment, wash up and tidy away all
equipment and tidy the bench space. Have the lab notebook and the tidy work space signed off by
a demonstrator before leaving the laboratory.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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SKILLS
BLOCK 1
EXPERIMENT 3A
DETERMINATION OF THE
Mr OF AN UNKNOWN
SOLID ACID
USING TITRATION
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SKILLS
EXPERIMENT 3A
3A. Determination of the Mr of an unknown solid acid using titration
In Experiment 2A, many of the issues that can arise when planning an experiment to collect good
quality data are explored. Certain experimental techniques have evolved over time to give an
agreed standard procedure that chemists can follow to produce results that are precise, accurate
and reliable (assuming the procedure is followed carefully). These procedures take account of all
the issues explored in experiment 2A. Learning how to perform these standard procedures is a key
part of your training as a good practical chemist. The procedures in this experiment include the
preparation of a standard solution and the use of titration. These procedures should be familiar to
you from your previous studies, but it is important that you follow the pre-lab exercises through
from start to finish to revise the methods and to be fully prepared for your laboratory class.
3A.1 Pre-lab exercises
These exercises must be completed at least one hour before the start time of the laboratory
session. Students not completing the pre-lab exercises task will be turned away from the laboratory
until the exercises are completed.
1. If completing this activity in Week 2, ensure that all the post-lab exercises from the first
laboratory session are completed. This includes setting up the lab notebook ready for use.
2. Read your Experiment Information carefully and highlight unfamiliar words or apparatus.
3. In DUO, in the Core Chemistry 1A Laboratory Course section, open ‘Foundation Chemistry
LabSkills’ and click to begin. Click on the ‘Equipment Glossary’ or the ‘Reagent Glossary’ at
the top of the screen to find the meaning of any unfamiliar words contained in your
laboratory manual.
4. Under the ‘Quantitative analysis’ sub-heading, move the cursor over ‘Titration’ and then
select ‘Video’ from the pop-up list. Watch each of the video clips in turn to familiarise
yourself with the technique.
5. Return to the main menu and again move the cursor over ‘Titration’. This time, select
‘Technique’ and work through the buttons on the yellow and blue bar at the bottom,
beginning with reading the ‘What is titration’ introduction page, then completing the
interactive exercises in ‘Setting up equipment’, ‘Taking readings’, ‘Finding an End-Point’ and
‘Analysing results’. Keep working through these until you have practiced and are
comfortable with the required procedure for the experiment. This includes being
comfortable with the calculations you will be required to do. You may find it helpful at this
point to write a more detailed method into the lab notebook, using the information
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provided on LabSkills and the Experiment Information provided in this laboratory manual,
ready for use in your laboratory session. This will ensure that you are able to work
independently and confidently. You should also plan or prepare your results table ready for
use during your experiment.
6. The accepted uncertainty in the laboratory burettes is ±0.05 cm3. This means that the
glassware has been manufactured to guarantee that any reading taken using it will be within
0.05 cm3 of the true value. Thus the burettes should be read to the
nearest 0.05 cm3 (and not any values in between). LabSkills allows you to
practice reading a burette before arrival in the laboratory. Practice this on
LabSkills to perfect technique (this task is not assessed so take as many
attempts as required to ensure that readings are being done correctly).
Look at the picture in Figure 3A.1. It can be seen that the meniscus sits just
below 1.40 cm3, but not as far as 1.45 cm3. It is, however, closer to 1.40
cm3, thus this is the reading from this burette. Remember to record this
value in the results table to 2 decimal places. i.e. for the reading in Figure
1, the results table would show a value of 1.40 cm 3, not 1.4 cm3. All
readings in the results table should be of the form X.X0 cm 3 or X.X5 cm3.
Remember to record readings to this level of precision during the
Figure 3A.1
experiment.
7. View the ‘Safety’ section from the ‘Titration’ menu and ensure you have clicked on all
information points to read about the safety aspects of your experiment.
8. From LabSkills Main Menu, go to the ‘Basic Skills’ section on the right hand side, and select
‘Preparing Solutions’. Work through all of this revision material to prepare for making the
standard solution of Acid A during the experiment. It may also be useful to read and view
the ‘Acid/Base Titration’ section (under ‘Titration’ and then ‘Common Experiments’).
9. Complete the pre-lab quiz (available on DUO in the Experiment 3A folder). Results for the
first attempt at this test will be stored and will count towards the summative mark for the
pre-lab. Review all the answers after completion of the test to receive feedback on the
responses and corrections to any mistakes.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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3A.2 Aims
 To practice appropriate use of titration apparatus following the accepted procedure
 To prepare a standard solution following the accepted procedure
 To use acid-base titration to determine concentration of an unknown
 To use acid-base titration to determine the Mr of an unknown solid acid
 To use an analytical balance
3A.3 Risk assessment
CHEMICAL RISKS
RISKS
SAFETY
Hydrochloric acid
At this concentration, treat as irritant.
Wear gloves.
Sodium hydroxide
At this concentration, treat as irritant.
Wear gloves.
Unknown Acid A
Treat as hazardous. Do not allow
contact with eyes or skin.
In case of contact rinse
immediately with plenty of water.
Wear suitable protective clothing
and gloves when handling.
Phenolphthalein
Limited evidence of a carcinogenic
effect. Irritating to eyes, respiratory
system and skin.
Wear suitable protective clothing
and gloves.
3A.4 Laboratory activity
Please note that the analytical glassware such as volumetric flasks, glass pipettes and burettes
should not be placed in the ovens as this can distort the glass and thus affect the calibration of the
apparatus. Only less accurately calibrated glassware, such as beakers, conical flasks, Quick-fit and
test tubes, should be placed in the glass oven.
This experiment revises techniques you will have learned before arriving in Durham. You will
therefore perform this experiment on your own. In Part 1 you will standardise (determine the
concentration of) a solution of sodium hydroxide using a solution of hydrochloric acid of known
concentration. In Part 2 you will make up a standard solution of unknown solid acid A, and use the
standardised solution of sodium hydroxide to perform a further titration to allow you to calculate
the Mr of acid A.
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Part 1 – Standardisation of the NaOH solution
Choose a work area with a free locker, and write the locker number at the top of the lab
notebook page for this experiment. You must also inform the demonstrator of the locker
number. Following the procedure outlined and practiced in the LabSkills software during the prelab exercises, titrate 25.00 cm3 aliquots of the NaOH solution (to be standardised) against the
hydrochloric acid solution of known concentration. Use two to three drops of phenolphthalein as
the indicator. Record the volume at the end point and calculate the titre value. This is the rough
titre. Using the rough titre as a guide, repeat the titration more carefully until two consecutive,
concordant (±0.05 cm3) results are obtained. This will take a minimum of three titrations, or it may
take more if the titration is not performed very carefully. Ask the supervising demonstrator to
check one of your end point readings. Use the results from your titration to calculate the
concentration of the sodium hydroxide solution and record to 3 significant figures. Use this value in
calculating your answer to Part 2. Show your value for the concentration to the demonstrator to
assess and note down.
Part 2 – Determination of the Mr of acid A
Record the mass of an empty weighing bottle and lid on an analytical balance. Then place the bottle
on a top pan balance and tare (set it to zero). Add between 1.9 g and 2.1 g of acid A to the bottle
(ensure the mass is within this range). Place the lid back on the weighing bottle and return it to the
analytical balance and record the mass of the weighing bottle, lid and acid A. Transfer the acid A to
a 250 cm3 beaker. Re-weigh the weighing bottle and lid (and any residual acid A) using an analytical
balance and record the mass. Determine the mass of acid A in the beaker.
Fully dissolve the solid acid A in no more than 100 cm3 of deionised water before transferring the
solution carefully and quantitatively to a 200.00 cm3 volumetric flask. Transfer the washings from
the beaker to ensure all the acid A is transferred to the volumetric flask. Make the solution up to
the mark and ask the supervising demonstrator to check that the meniscus is on the line. Once
checked, stopper the flask and invert a number of times to mix thoroughly.
Using the technique revised on LabSkills, titrate 20.00 cm3 aliquots of the sodium hydroxide
solution used in Part 1 (now of known concentration) with this freshly prepared solution of acid A,
using phenolphthalein as the indicator. Repeat until two consecutive titrations differ by no more
than 0.05 cm3. Remember to read the burette to the nearest 0.05 cm3 and record your results to
two decimal places. Show the supervising demonstrator your titration results.
Assuming that acid A is a monobasic acid, calculate the amount (in moles) of acid A that reacts in
the titration with NaOH. Use this information, and the mass of acid A used to prepare the standard
solution, to calculate the relative molecular mass, Mr, of acid A. Report the result to an appropriate
degree of precision. Show your Mr value to the supervising demonstrator for them to assess and
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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note down. Acid A is an analytical standard, so it is anticipated that results will be in the range
±0.5% of the actual Mr.
Discard the remaining solution of acid A down the sink with plenty of water. Clean and wash all
equipment used, and leave apparatus in a good condition for the next person working in that area.
Ensure all taps are turned off. Ask a demonstrator to mark your lab notebook and to sign off your
tidy work space before leaving the laboratory. Ensure that the demonstrator has made a note of
the concentration of NaOH determined in Part 1, and the Mr value calculated in Part 2 before
leaving the laboratory.
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SKILLS
BLOCK 1
EXPERIMENT 3B
DETERMINATION OF THE
% PURITY OF A SAMPLE
OF OXALIC ACID
(ETHANEDIOIC ACID)
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SKILLS
EXPERIMENT 3B
3B. Determination of the % purity of a sample of oxalic acid (ethanedioic acid)
Oxalic acid (ethanedioic acid) is used as a wood-bleaching agent and in many types of rust remover.
The oxalic acid in the laboratory is an impure sample which also contains sodium oxalate. The %
purity of the sample can be determined by using a simple acid-base titration. The oxalic acid used
exists in solid form as the dihydrate, meaning there are two moles of water of crystallisation per
mole of oxalic acid (C2H4O2.2H2O).
3B.1 Pre-lab exercises
These exercises must be completed at least one hour before the timetabled start time of the
laboratory session. Students not completing the pre-laboratory task will be turned away from the
laboratory until the exercises are completed.
1. Read the laboratory activity through carefully and highlight unfamiliar words or apparatus.
2. In DUO, in the Core Chemistry 1A Laboratory Course section, open Foundation Chemistry
LabSkills and click to begin. Click on the ‘Equipment Glossary’ or the ‘Reagent Glossary’ at
the top of the screen to identify any unfamiliar words contained in your laboratory script.
3. Use LabSkills to go over the techniques required, including ‘Titration’, ‘Preparing Solutions’
and ‘Weights and Measures - Using a Pipette’.
4. Prepare the lab notebook for the session. The structure of the oxalic acid should be drawn
out and the equation for the titration between oxalic acid dihydrate and sodium hydroxide
will need to be deduced and written out. An expanded method, designed using your
previous experiment and LabSkills to assist, will need to be written out in full. This should
include details of all the information needed to carry out the experiment independently.
5. Ensure that the calculation required for the analysis of the results from the experiment has
been practiced.
3B.2 Aims
 To prepare a standard solution and to determine the % purity of a sample of oxalic acid by
titration
 To practice titration calculations in different contexts
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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3B.3 Risk assessment
CHEMICAL
RISKS
SAFETY
Oxalic acid
(ethanedioic acid)
Sodium hydroxide
Phenolphthalein
Harmful in contact with skin, eyes and if
swallowed. Do not breathe dust.
At this concentration, treat as irritant.
Limited evidence of a carcinogenic effect.
Irritating to eyes, respiratory system and skin.
Wear gloves and eye
protection.
Wear gloves.
Wear suitable protective
clothing and gloves.
3B.4 Laboratory activity
This experiment allows for further practice at using titration to solve a problem. Experimental
instructions will be very brief to ensure that the procedure is well understood. A longer, more
detailed method should have been written into the lab notebook as part of the pre-lab exercises.
Laboratory work will again be performed individually to further develop practical confidence.
1. You will be working individually for this experiment. Choose a work area with a free locker,
and write the number at the top of the lab notebook page for this experiment. Inform the
demonstrator of the locker number and show the prepared lab notebook.
2. Prepare a 250.00 cm3 standard solution containing between 1.50 g and 1.70 g of impure
oxalic acid. Ensure the mass of impure oxalic acid is known and recorded to at least 3
decimal places. Show a demonstrator the mass of acid recorded. Warm the impure oxalic
acid gently in the beaker to aid dissolving, if necessary, using a hotplate. When the solution
has been made up to the line in the 250.00 cm3 volumetric flask, show a demonstrator
that the meniscus is on the line before adding a bung and shaking the solution.
3. Titrate the solution with 25.00 cm3 aliquots of standardised 0.100 M sodium hydroxide
solution. Record results appropriately. Show a demonstrator one burette reading, from
somewhere in the middle of the burette. Show a demonstrator the titration results.
4. Using the titration results, determine the percentage purity of the oxalic acid solid. Show
your % purity value to the supervising demonstrator.
5. Calculate the % error in your result (compared to the suggested % impurity provided by a
demonstrator). Calculate the total apparatus error for your experiment. Comment on the
values and their meaning for the experiment. Does your experiment show that the
suggested % impurity for the sample of oxalic acid is correct? Show a demonstrator the
answers for this section.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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6. Wash up and put away all equipment. Ensure locker space is tidy. Ask a demonstrator to
sign off your locker and work space.
7. Work through the following exercises in the lab notebook. These exercises are designed to
provide additional practice in stoichiometric calculations. Ensure that appropriate balanced
equations are written out and that calculations are shown in full. Show a demonstrator the
answers to the exercises before leaving the laboratory.
Exercise 1
5.125 g of washing soda crystals (Na2CO3.xH2O) are dissolved in water, and the resulting solution
was made up to 250.00 cm3. 25.00 cm3 of this solution required 35.80 cm3 of 0.0500 mol dm-3
sulfuric acid for neutralisation. Calculate the percentage of sodium carbonate in the crystals and
determine a value for x in the formula Na3CO3.xH2O.
Exercise 2
5.032 g of a dibasic organic acid (H2A) with an anhydrous relative molecular mass of 90 was
dissolved in water and the solution was made up to 1.000 dm3. 25.00 cm3 of this solution required
19.97 cm3 of 0.1000 mol dm-3 sodium hydroxide for complete neutralisation, using phenolphthalein
as an indicator. Calculate the number of moles of water of crystallisation per mole of acid.
Exercise 3
3.000 g of a mixture of sodium carbonate and sodium chloride were dissolved in water and the
solution was made up to 250.00 cm3. 25.00 cm3 of this solution required 21.00 cm3 of 0.1050 mol
dm-3 hydrochloric acid for neutralisation. Calculate the % by mass of the sodium chloride in the
mixture.
Exercise 4
0.500 g of impure ammonium chloride is warmed with an excess of sodium hydroxide solution. The
ammonia liberated by this reaction is reacted with 25.00 cm3 of 0.2000 mol dm-3 sulfuric acid. The
excess acid required 5.64 cm3 of 0.2000 mol dm-3 sodium hydroxide for neutralisation. Calculate the
percentage of ammonium chloride in the original impure sample.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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SKILLS
BLOCK 1
EXPERIMENT 4A
PURIFICATION OF AN
UNKNOWN SOLID
BY RECRYSTALLISATION
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SKILLS
EXPERIMENT 4A
4A. Purification of an unknown solid by recrystallisation
In this experiment you will be recrystallising an impure solid. This is a common purification
method.2 The purpose of recrystallisation is to remove both soluble and insoluble impurities from a
solid. To do this, a solvent must be found in which the bulk of the material will dissolve when it is
hot but not when it is cold. The insoluble impurities can then be filtered from the hot solution. On
cooling, the desired material crystallises leaving the soluble impurities still in solution. The pure
compound can therefore be filtered from the cold solution. You will be using reflux apparatus and
handling other common laboratory apparatus. Some of these techniques may be familiar to you
from your pre-University studies, but it is important that you follow the pre-lab exercises through
from start to finish. This will allow you to revise the procedures and prepare for the laboratory
class.
4A.1 Pre-lab exercises
These exercises must be completed at least one hour before the timetabled start time of the
laboratory session. Students not completing the pre-laboratory task will be turned away from the
laboratory until the exercises are completed.
1. If completing this activity in Week 2, ensure that all the post-lab exercises from the first
laboratory session are completed. This includes setting up the lab notebook ready for use.
2. Read the instructions in your laboratory manual through carefully and highlight unfamiliar
words or apparatus.
3. In DUO, in the Core Chemistry 1A Laboratory Course section, open Foundation Chemistry
LabSkills and click to begin. Click on the ‘Equipment Glossary’ or the ‘Reagent Glossary’ at
the top of the screen to identify any unfamiliar words contained in the laboratory manual.
4. Preparing for the recrystallisation: Under the ‘Preparation and Purification’ sub-heading,
move the cursor over ‘Recrystallisation’ and then select ‘Technique’ from the pop-up list.
Read the first page about recrystallization, and practice the simulation on the second page
until you have successfully recrystallized the solid. Then select ‘Video’ and watch the
procedure again, and then select ‘Safety’ and read through the safety points, focusing
particularly on use of stirrer hotplates.
2
For further information about recrystallisation, see pp92-101 of Dean, J. R. et al, ‘Practical Skills in Chemistry’, (2002),
Prentice Hall or p127 of Harwood, L. M. and Moody, C. J., ‘Experimental Organic Chemistry: Principles and Practice’
(1989), Blackwell Scientific Publications.
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5. Preparing for using reflux apparatus: Solids can be recrystallised from water using a conical
flask and stirrer hotplate, as shown in the simulation in LabSkills or, for more volatile and
flammable solvents, alternative apparatus can be used. The solid in this experiment,
although being recrystallised from water, will be dissolved using reflux apparatus to provide
students with experience in setting up this glassware. It would, however, be more usual3 to
use reflux apparatus for more volatile and flammable solvents than water! To become
familiar with the required apparatus, go back to the Main Menu of LabSkills and under the
‘Preparation and Purification’ sub-heading, move the cursor over ‘Reflux’ and then select
‘Video’ and watch the procedure. Next, select ‘Technique’ and read about the use of the
apparatus and then have a go at setting it up using the simulation. Keep practising with the
simulation until you have successfully reached reflux. Remember that this experiment still
involves a simple recrystallisation, just using reflux apparatus instead of a conical flask.
Finally, view the safety information provided about reflux apparatus.
6. From the Foundation Chemistry LabSkills main menu, select ‘Filtration’. Select ‘Technique’
from the menu and read through the information, clicking along the progress bar at the
bottom to move through. When complete, click on ‘Gravity Filtration Video’ and watch all
stages, then click on ‘Buchner filtration video’ and watch through. Both of these methods of
filtration should be familiar from prior studies, but, if not, take time to learn about the
differences between them and their uses.
7. Preparing for taking a melting point: Select ‘Melting Point’ from the LabSkills main menu
and read about the technique, watch the video and read the safety information thoroughly.
Practice taking a melting point using the simulation. No further instructions will be provided
about taking a melting point in this laboratory manual, so use LabSkills thoroughly to
prepare for the experiment.
8. It is likely that previous practical work has usually required the use of a Bunsen burner for
heating. In the undergraduate laboratory, it is more likely that a hot plate will be used,
accompanied by a magnetic stirrer bar (also known as a ‘stir flea’). To prepare for using this
apparatus, open the Chemistry Interactive Lab Primer, either via DUO or using a web
browser (http://chem-ilp.net). Select the ‘Lab Techniques’ tab and select ‘Heating’ from the
menu. Click on ‘Hot Plates’ and read all information about the use of stirrer hotplates and
magnetic stirrer bars.
9. Prepare the lab notebook ready to begin the laboratory session. This should include drawing
diagrams of reflux apparatus and Buchner filtration apparatus and any necessary notes
3
See p96 of Dean, J. R. et al, ‘Practical Skills in Chemistry’, (2002), Prentice Hall for further discussion.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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about taking a melting point to assist during the experiment. The diagrams will not be
provided in the laboratory manual.
4A.2 Aims
 To develop confidence with use of reflux apparatus
 To purify an unknown solid by recystallisation
 To practice using different methods of filtration
4A.3 Risk assessment
CHEMICAL
RISKS
SAFETY
Unknown solid
Harmful. Irritant.
Wear suitable protective clothing and gloves.
4A.4 Laboratory activity
1. Work in pairs for this experiment. Choose a work area with a free locker and select a fume
cupboard. Write the number of these at the top of the lab notebook page for this
experiment. Inform the demonstrator of the locker and fume cupboard number.
2. Using a weighing bottle or weighing boat, weigh out approximately 2.0 g of impure solid.
Over a piece of paper, carefully transfer the solid to a 100 cm3 B19 round bottomed flask.4
Keep a small amount in the weigh bottle for melting point determination. Record the mass
of impure solid used.
3. Add 20 cm3 of deionised water and a magnetic stirrer bar. Set up the apparatus for heating
at reflux as practised in the pre-lab exercises. Show a demonstrator the reflux equipment
set-up before switching on the heat source. Heat the mixture using a hotplate and heating
block with hotplate on full. Once reflux has been reached, remove from the hotplate,
observe how much solid material is remaining, add more water (5 cm3) down top of
condenser and re-heat. Repeat this process until no more solid material dissolves. Note that
not all of it will dissolve because the sample contains a solid impurity. Remember that
recrystallisation involves the use of the minimum amount of solvent to prepare a saturated
solution, so do not add too much.
4. Filter the hot saturated solution through a fluted filter paper (see Appendices 1 and 2, page
37) in a pre-heated large filter funnel into a preheated, insulated 100 cm3 conical flask. This
4
‘B19’ indicates the size of the glass joint on the flask. All of our glassware is ‘B’ and is typically B10, B14, B19 or B24 in
size. The numbers indicate the diameter of the joint. Thus a B19 joint is larger in diameter than a B10 and B14 but
smaller than a B24. The size is often indicated near the neck of the glassware.
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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process removes insoluble materials (e.g. dust). If the product crystallises in the filter paper,
add a small amount of boiling water and allow it to filter. Repeat until the crystals are fully
through the filter paper.
5. Allow the saturated solution to cool slowly in the insulated flask, whereupon crystals will
form.5 Show a demonstrator the crystals in the conical flask. Filter this solution using a
Buchner funnel, and when all the liquid phase is just disappearing, wash the crystals on the
filter paper with fresh, cold water, keeping the vacuum on and still sucking. Suck the
crystals as dry as possible and press down the crystals with a stopper or spatula. Transfer
the crystals to a pre-weighed watch glass and dry by gently pressing a filter paper down
onto the crystals until they are as dry as possible. If they are very wet, place in an oven on
the watch glass for half an hour (ensure that the oven is not too hot). Record the mass of
the dry crystals. Show a demonstrator the crystals produced, and the mass recorded.
6. Determine the melting point of the recrystallised material and the impure starting material.
Follow the procedure practised on LabSkills: Fill melting point tubes with each of the two
materials and perform a rough determination of the melting point of one by heating rapidly
(i.e. at the maximum rate); observe the tube closely through the viewfinder and note the
approximate melting temperature. Cool the heating block to 20 oC below the approximate
melting point, insert a fresh tube and reheat SLOWLY. Record the temperature at which the
solid first begins to melt, and the temperature at which it has all melted, i.e. a temperature
range. If time, perform accurate repeats of the melting point determination. If enough data
has been collected, report one single melting point for each solid. Show a demonstrator the
melting point results.
7. Wash up (where required) and put away all equipment. Ensure contaminated filter papers
are placed into the ‘solid waste’ receptacle provided, with all instructions about packaging
the waste followed carefully. Ensure locker space and fume cupboard is clean and tidy. Ask
a demonstrator to sign off the locker and work space.
8. Discuss the following questions within pairs and write answers into the lab notebook. Show
a demonstrator the lab notebook for discussion of answers and for signing off before
leaving the laboratory.
5
The solution remaining after recrystallisation is often referred to as the mother liquor. The crystals are usually isolated
from the mother liquor by filtration, leaving the mother liquor in the receiving flask (the filtrate).
First Year Chemistry Laboratory Course 2011-2012: SKILLS Block 1
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Question 1
What are the melting point criteria for judging whether an organic solid is pure?
Question 2
Which way does the melting point of an increasingly purified solid change – upwards or
downwards?
4A.5 Appendix 1 – Procedure for fluting a filter paper
1. Fold the paper in half and open it out flat again
2. Rotate through 90o and repeat step 1 (the paper is now folded in quarters)
3. Fold in half again so that two quarters are bisected (the easy way to do this is to match up
the previous folds) and again open it out flat.
4. Repeat step 3. Your paper should now be folded into eighths.
5. Turn the paper over.
6. Fold in half to bisect two of the eighths (again, match up some of the previous folds) and
open it out flat.
7. Rotate the paper and repeat step 6; keep going until all the eighths have been folded in half.
Your paper should now be in sixteenths, with each alternate fold going the opposite way.
8. Fold your paper into a concertina shape – you are now ready to filter!
A video demonstrating how to flute a filter paper is available on DUO. If you are struggling with the
origami, you might want to use a free computer in the laboratory and follow along with the video
to fold your paper.
4A.6 Appendix 2 – Procedure for performing a hot gravity filtration
1. Line a large beaker with a duster and insert your conical flask and filter funnel.
2. Prepare a fluted filter paper as in Appendix B; place it in the filter funnel
3. Place the whole set up in a hot oven and leave for about 10 min.
4. Carry out the filtration of the hot solution immediately; place a filter paper over the mouth
of the funnel between additions of solution to slow down the rate of cooling.
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SKILLS
BLOCK 1
EXPERIMENT 4B
PREPARATION OF
CYCLOHEXENE
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SKILLS
EXPERIMENT 4B
4B. Preparation of cyclohexene
This experiment involves the dehydration of cyclohexanol using sulfuric acid to form cyclohexene.
4B.1 Aims
 To produce cyclohexene using an azeotropic distillation
 To purify cyclohexene using solvent extraction (a separating funnel), a drying agent and a
further distillation
 To test a chemical property of cyclohexene
4B.2 Pre-lab exercises
These exercises must be completed at least one hour before the timetabled start time of the
laboratory session. Students not completing the pre-laboratory task will be turned away from the
laboratory until the exercises are completed.
1. Read your laboratory instructions through carefully and highlight unfamiliar words or
apparatus.
2. In DUO, in the Core Chemistry 1A Laboratory Course section, open Foundation Chemistry
LabSkills and click to begin. Click on the ‘Equipment Glossary’ or the ‘Reagent Glossary’ at
the top of the screen to identify any unfamiliar words contained in your laboratory manual.
3. Preparing for the distillation: Using LabSkills, under the ‘Preparation and Purification’ subheading, move the cursor over ‘Distillation’ and then select ‘Technique’ from the pop-up list.
Read the first page about distillation, and use the simulation on the second page to practice
setting up distillation apparatus. Then select ‘Video’ and watch the procedure again, and
then select ‘Safety’ and read through the safety points, focusing particularly on the use of
stirrer hotplates. It may also be useful to look through the relevant sections on the
Chemistry Interactive Lab Primer (http://chem-ilp.net) if this technique has not been used
before.
4. Preparing for use of a separating (or separatory) funnel: Using LabSkills, under the
‘Preparation and Purification’ sub-heading, select ‘Solvent Extraction’ and read the
introduction about the use of a separating funnel. Watch the video demonstrating the use
of a separating funnel. Use the simulation to practice using the separating funnel, and read
about the drying liquids. Read through and pay close attention to the safety aspects of the
procedure. It may also be useful to look through the relevant sections on the Chemistry
Interactive Lab Primer (http://chem-ilp.net) if this technique has not been used before.
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5. Prepare the lab notebook. Include any required notes about the method, and draw
diagrams of distillation apparatus using LabSkills or the Interactive Lab Primer to assist. Use
the glossary in the Interactive Lab Primer to write a definition of an azeotrope. Also include
a copy the reaction scheme (below), and identify intermediate A. Explain why the
experimental set-up allows the reaction to be driven to completion.
4B.3 Risk assessment
CHEMICAL
RISKS
SAFETY
Cyclohexanol
Harmful by inhalation and if
swallowed. Irritating to
respiratory system and skin.
Avoid contact with skin and eyes.
Cyclohexene
Highly Flammable. Harmful
in contact with skin and if
swallowed.
Keep away from sources of ignition. Do not
empty into drains. Wear suitable protective
clothing and gloves
Bromine
Very Toxic by inhalation.
Causes severe burns. Very
Toxic to aquatic organisms.
In case of contact with eyes, rinse
immediately with plenty of water. Avoid
release to the environment. Keep container
tightly closed and in a well-ventilated place.
Sulfuric acid
Causes severe burns.
Corrosive.
Sodium carbonate
Irritant.
In case of contact with eyes, rinse
immediately with plenty of water. Never
add water to this product Wear gloves. Use
in fume cupboard.
Do not breathe dust. In case of contact with
eyes, rinse immediately with plenty of
water.
Dichloromethane
Limited evidence of a
carcinogenic effect.
Do not breathe gas/fumes/vapor/spray.
Avoid contact with skin and eyes. Wear
suitable protective clothing and gloves.
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4B.4 Laboratory activity
You will be working in pairs for this experiment, and working in a fume cupboard throughout.
Choose a work area with a free locker and select a fume cupboard. Write the number of these at
the top of the lab notebook page for this experiment. Inform the demonstrator of the locker and
fume cupboard number.
1. Wear gloves throughout the experiment, and work in a fume cupboard throughout.
Carefully add 6 cm3 of concentrated sulfuric acid to 50 g (0.50 mol) of cyclohexanol in a 250
cm3 round bottomed flask and then mix the contents by swirling gently. Add a magnetic
stirrer bar and equip the flask with a condenser and 110 °C thermometer, ready for
distillation. Show a demonstrator the distillation set-up before commencing heating.
2. Heat the flask using a hotplate and heating block at such a rate that the temperature of the
distillate remains below 95 °C. Collect the distillate in a 100 cm3 beaker and stop when the
residue in the flask starts to evolve white fumes. Record the volume of water in the
distillate (by transferring it to a measuring cylinder) in the lab notebook. Show a
demonstrator the product (keeping it in the fume cupboard).
3. In a fume cupboard, place the entire distillate in a separating funnel, and wash successively
with a 20 cm3 portion of water, a 20 cm3 portion of 10% sodium carbonate solution and
once again with 20 cm3 of water. Keep the organic layer after each washing, and discard the
aqueous phase into a conical flask (not down the sink until it is clear that the product has
been isolated and no mistakes have occurred).
4. In a fume cupboard, transfer the organic phase to a 125 cm3 conical flask, add anhydrous
MgSO4 and swirl the mixture in order to dry the solution. Fit a cork or rubber stopper and
leave for 10 minutes. Show a demonstrator the dry organic phase.
5. In a fume cupboard, filter the solution into a 100 cm3 round bottomed flask, add a magnetic
stirrer bar, and set up distillation apparatus. Ensure that the receiver flask is pre-weighed
with a stopper and the mass noted. Perform a distillation to obtain the cyclohexene
product, which has a boiling point below 100 °C. Note the boiling point range of the product
in the lab notebook. Record the mass of the cyclohexene collected, and calculate the % yield
for the experiment, showing the overall equation for the reaction and any calculations.
Calculate the theoretical maximum amount of water that could have been obtained from
this reaction. Show a demonstrator the results.
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6. In a fume cupboard, test the reaction of the product with bromine. To do this, add
approximately 1 cm3 of dichloromethane to a test tube. Add 5 drops of the distilled product,
shake well, then add 10 drops of bromine solution in dichloromethane. Shake well (use a
bung) and record observations in the lab notebook, including a comparison to the original
colour of the dichloromethane solution.
7. Identify intermediate B and the product C of the following reaction between cyclohexene
and bromine. Draw this scheme into the lab notebook, but give the structure of B and C and
give curly arrows to show the formation of B. Use wedged/dashed bonds to show the
stereochemistry of the product. Show a demonstrator the lab notebook.
8. Consider the purification of the crude cyclohexene obtained after Step 3. Discuss in pairs
how each of the following contaminants were removed from the cyclohexene before the
final distillation: (a) cyclohexanol, (b) sulfuric acid, (c) water. It may be helpful to check the
solubilities of these substances using the CRC Handbook available in the laboratory. Note
down how each substance was removed in the lab notebook. Show a demonstrator the lab
notebook.
9. Dispose of all waste appropriately. Organic liquids should be disposed of in the Category C
waste, and dichloromethane should be placed in the Category D waste. Wash apparatus
carefully to avoid any fumes escaping. Put away all equipment and tidy the fume cupboard
and the work bench and lab locker. Ask a demonstrator to sign off the fume cupboard,
bench space and lab locker before leaving the laboratory.
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4B.5 Appendix 1 – Setting up a distillation
Assemble the apparatus as shown below.
Notes:




Remember to run the condenser water in at the bottom and out at the top.
Have the water flowing SLOWLY through the condenser
Use plastic clips or elastic bands, if required, to secure the receiver adapter to the end of the
condenser
If the thermometer is a conventional one that is connected by way of a thermometer
adaptor, make sure that the thermometer bulb is level with the start of the side arm of the
still head (the bit that connects the flask to the condenser!) to get a reasonable temperature
reading
To perform the distillation:
1. Heat flask with crude mixture to above the boiling point.
2. Monitor the temperature as the material starts to distil over; wait until the temperature
stabilises, then record this temperature.
3. Monitor the temperature throughout the distillation and record the highest temperature.
4. Stop the distillation when most of the material has distilled (there will always be some
undistillable residues left in the flask).
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APPENDIX A: Assessment guide for laboratory reports
Reports will be assessed against the following criteria, which are not necessarily equally weighted.
First
Class
Structure
Presentation
Technical Content
Results and
Discussion
Excellent, very clear,
logical subdivision.
Well written in good
English, cogent
arguments presented.
Conclusions concur
with results obtained,
results are clearly
summarised.
Appropriate
theoretical
background included.
Proper use made of
theory expressions,
etc.
Critical assessment of
the results. Quality of
sample based on data
(spectra, errors).
Graphs neatly plotted
and correctly
interpreted. Extended
interpretation based
on analysis of theory
section.
Results analysed and
assessed in sufficiently
critical manner.
Evidence of an
appreciation of
sources of error.
Satisfactory
assessment of results
and outcome of
experiments. Critical
evaluation not overly
evident.
Poor analysis of the
results or sample
quality, no attempt to
assess sources of error
or where things may
have gone wrong.
No assessment of the
results, no discussion.
Upper Well organised easy to Clearly laid out,
Second follow and a sense of conclusions and
direction throughout.
summary evident and
clearly written.
Good grasp of the
necessary theory and
its use.
Lower Satisfactory but some
Second loss of way evident.
Straightforward to
read, satisfactorily
written, vagueness or
hesitancy in
conclusions and
summary.
Somewhat
disorganised and hard
to read. Conclusion
and summary
incorrect or “off the
mark”.
Difficult to read; slap
dash presentation,
absence of conclusion
or summary.
Only the basic theory
behind the
experiment is
presented, no
evidence of real
understanding.
Gaps in understanding
evident from what
was presented.
Third
No direction, no
subdivision. Lack of
clarity.
Fail
No evidence of any
organisation, absence
of basic
understanding, no
coherence.
No real presentation
of background and its
appreciation.
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